Synthetic methods have been developed for producing a wide variety of nanostructures that differ in size, shape, and composition. Methods now exist for preparing nonspherical, monodisperse samples of Au and Ag triangular prisms,(1-5) cubes,(6,7) wires,(8) bars,(9) tetrahedra,(7,10) octahedra,(11) decahedra,(12,13) bipyramids,(14) and disks.(15) Synthetic control over particle shape allows one to chemically tailor the optical, electric, magnetic, and catalytic properties of such structures, making them useful for many applications, including biological diagnostics,(16) therapeutics,(17) catalysis,(18,19) and optics.(20,21)
One of the most controllable synthetic methods for making anisotropic nanostructures involves the photochemical conversion of silver (Ag) spheres into triangular prisms.(1) With this synthetic method, the growth of the silver nanoprisms can be modulated through a combination of photoexcitation and pH control,(2,22) and the resulting edge length of the nanoprisms can be controlled by excitation wavelength. The prisms grow via a photo-mediated process until their plasmon resonances are red-shifted from the excitation wavelength. This method has been widely used to synthesize silver nanoprisms and other related structures (e.g., nanodisks or truncated prisms).(23-26) In addition, even more exotic structures, such as decahedra and tetrahedra can be realized through plasmon-mediated syntheses, although wavelength driven size control has not been demonstrated with these particle shapes.(10,13)
The use of plasmon excitation to control nanostructure growth has significant advantages over thermal methods. Most notably, it allows one to control particle size and reaction rate simply through choice of excitation source and wavelength. The photogeneration of triangular silver prisms is one of the excellent examples of the utility of such methods. Indeed, one can generate equilateral triangular prisms with a fixed thickness and an edge length which is tunable over the 40 to 120 nm range simply by choice of excitation wavelength and pH. This system, although impressive, is the only example to date where excitation wavelength driven particle size control has been demonstrated.